1. Field of the Invention
The present invention relates to a precharge controlling method, and a display device using the same.
2. Description of Related Art
A capacitive coupling drive system is known as a system for driving a display device, for example, a liquid crystal display device. In the liquid crystal display device using the capacitive coupling drive system, pixel portions each of which is composed of a switching element, a liquid crystal pixel cell, and a coupling capacitor Cs are formed so as to correspond to intersection portions in which scanning lines and signal lines intersect with each other, respectively. In this case, an offset voltage is applied as a potential to the pixel cell by using the coupling capacitor Cs after a video signal Vsig is written to the pixel cell, thereby driving the pixel cell. This technique, for example, is described in Japanese Patent Laid-Open No. 2001-255851. That is to say, the coupling capacitor Cs is driven by using a necessary voltage (hereinafter referred to as “a coupling voltage”) Vcs after the video signal Vsig is written to the pixel cell, and the pixel cell is driven by using a pixel potential obtained by adding the video signal Vsig and the coupling voltage Vcs to each other. According to the capacitive coupling drive system, the video signal Vsig can be written to the pixel cell at a high speed and the low power consumption can be realized because of a small amplitude of the video signal Vsig.
A pixel potential Vpix applied to the pixel cell when the capacitive coupling drive is carried out is expressed by Expression (1):Vpix=Vsig+(Cs/(Cs+Clc))×Vcs  (1)
where Vpix is the pixel potential, Vsig is the video signal (an amplitude of the video signal on the signal line), Cs is a coupling capacitance of the coupling capacitor, Clc is a capacitance of the liquid crystal cell with a counter electrode, and Vcs is the coupling voltage with which the coupling capacitor Cs is driven. Here, Expression (1) is described in Japanese Patent Laid-Open No. 2007-47221.
Heretofore, the coupling voltage with which the coupling capacitor Cs is driven is set at a certain fixed potential. However, as shown in Expression (1), the pixel potential Vpix depends on a capacitance ratio of the coupling capacitance Cs to a sum of the coupling capacitance Cs and the holding capacitance Clc of the pixel cell. As a result, the manufacture dispersion and the fluctuation of the relative permittivity due to the ambient temperature cause the reduction in yield, and the deterioration of the image quality. A method devised in order to cope with such a situation is described in Japanese Patent Laid-Open No. 2007-47221. According to this method, the coupling voltage Vcs is controlled, so that the coupling capacitance Cs is driven by using the optimal coupling voltage Vcs without depending on the manufacture dispersion and the ambient temperature (the so-called environmental temperature).
Also, Japanese Patent Laid-Open No. 2005-99170 discloses a precharge operation of a drive circuit which will be described later.